This post is part of a larger discussion about temporal databases.  Hopefully it stands on it’s own but for more context see the Temporal Database Design page.

Most of us have worked with database tables that track some historical information.  You add a EffectiveDate column or something similar and usually it’s just limited to a table to two.  A Temporal Database is designed so most or all of the tables can track historical information.

The important part is that you can access the historical database using a SQL query and don’t have to look elsewhere, such as audit log.  This is what makes a database a Temporal Database, at least according to me.

Degree of Database Temporalness

A database can either be non-temporal, partial temporal, or fully temporal.  You can measure the temporalness by the percentage of tables that store temporal data.

Non-Temporal (0% Temporalness): Database has no temporal capabilities.

Partially Temporal (1% - 99% Temporalness): The database has some tables store temporal data but not all.

Fully Temporal (100% Temporalness): All the tables in the database store temporal data.

Type of Table Temporalness

We don’t measure how temporal a table is by percentage.  Instead a table is defined by what type of historical data you can retrieve.  There are two types of historical data:

You can read the official Wikipedia definition but for our purposes it’s a database where you can query for historical data using SQL.

For example, say you have someone named Chronos who lives in New York but on April 15, 2012 moves to Hong Kong.  If you don’t have an historical tracking then you will only be able to see that Chronos lives in Hong Kong.  You don’t know where he lived before Hong Kong or when he moved to Hong Kong.

In Part 1 we created a custom NUnit constraint but you where limited in using the constraint.  You could only write:

 
// Instantiate the constraint. 
Assert.That(expected, new EquivalentPropertyWiseToConstraint(actual)); 

// Matches syntax. 
Assert.That(expected, Is.Not.Matches(new EquivalentPropertyWiseToConstraint(actual)));

It would be nice to write:

// Directly access the constraint from Is.
Assert.That(expected, Is.EquivalentPropertyWiseTo(actual));

// Chain the constraint in Is.
Assert.That(expected, Is.Not.EquivalentPropertyWiseTo(actual));

To do that you should read the documentation.  End of blog post.

So is that joke still funny?  No, OK, no more.  Lets get back to what we are doing.  To access the method using Is you need to override the Is class and add a static method.  I recommended making the method name similar to your constraint name.  For example:

NUnit has has built in constraints for most the tests you will need to write so there is no need to create your own.  End of blog post.

OK, that was a bad joke.  The first step in creating a NUnit custom constraint is to read the documentation.  That’s it.  End of blog post.

Not as funny as the first time?  Not funny at all?  I won’t use that joke again.  But you did read the documentation right?  OK, good.

A common unit test assert I need to do is compare all the property values of one object to another.  For example:

[Test]
public void TestSaveWorks()
{
  // Create a value to save.
  var expectedDto = new SomeDto() {ValueOne = 1, ValueTwo = "Blah"};

  // Save the value.
  _someDbService.Save(dtoToSave);

  // Load the value from the database.  The DTO ID
  // should have been set by the save.
  var actualDto = _someDbService.Find(expectedDto.Id);
  
  Assert.That(expectedDto.ValueOne, Is.EqualTo(actualDto.ValueOne));
  Assert.That(expectedDto.ValueTwo, Is.EqualTo(actualDto.ValueTwo));
}

In this test we only have two properties to test but if the object has 10 plus properties to test that would be quite onerous.   I often forget to update the tests after I add a new property to the object.